Slide guide assembly and slider kit for floating cover of digester tank and associated method

ABSTRACT

A guide assembly for a floating cover of a sludge digester tank includes a track having a pair of opposing surfaces facing one another to define a vertical guide channel or track connected to the tank or the floating cover. At least one slider member is disposed in the channel for vertical motion therein. The slider member is connected to the other of the tank or the floating cover. Two bearing strips are attached to the slider member for engaging opposing surfaces of the track in a low-friction slidable contact. The bearing strips are vertically removable from the slider member, so that the bearing strips may be replaced without removing the slider member from the guide channel.

BACKGROUND OF THE INVENTION

[0001] This invention relates to sludge digester tanks. More specifically, this invention relates to slide guide assemblies for guiding floating covers of digester tanks. This invention also relates to an associated slider kit utilizable in constructing such a slide guide assembly. In addition, this invention relates to a method for maintaining such a slide guide assembly of a sludge digester tank.

[0002] Sewage plant sludge is often collected and subjected to anaerobic digestion in tanks with floating covers that are vertically movable with volumetric changes of the liquid, gas, or both in the digester tanks. In one kind of floating cover tank, the cover floats directly on the liquid sludge and gas produced by the digesting sludge is removed through a gas take-off housing or is vented to the atmosphere. In another type of tank, a so-called gasholder cover traps gas produced in the sludge digestion process, whereby the cover floats above the liquid sludge on the gas.

[0003] In many types of sludge digester tanks, the vertical movement of the floating covers is aided and stabilized by a plurality of circumferentially interspaced, vertical slide guide assemblies. Each slide guide assembly comprises a stationary vertical column slider defining a vertical track or channel in which a slider member is slidably installed. The slider members are rigidly fixed to the tank cover, generally indirectly via a cylindrical skirt depending from the disk or dome-shaped cover. As the amount of gas in the tank increases, the slider members move upwardly along their respective columns.

[0004] In one kind of conventional slide guide assembly, the movement of the slider members in the channels of the guide columns is facilitated by metal rollers. It has been found, however, that rollers can evince substantial maintenance problems. Rollers can break, seize or disengage, which may result in a tilting of the tank cover or an arresting of the vertical float motion.

[0005] In an alternative solution, a pair of slider brackets is provided instead of metal rollers. One bracket is disposed on top of the tank cover and in vertical alignment, while the other bracket is disposed at the bottom of the tank cover skirt. The motion of the slider brackets is eased by the provision of bolted low friction polymeric bearing strips that come in contact with the inner surfaces of the guide channels. The replacement of the bearing strips requires disassembly of the entire slide guide assembly and in the case of the bottom assembly requires a disruption of the sludge treatment and processing operation.

[0006] In yet another alternative solution, where a slider member moves along a vertical channel in a guide track, the motion of the slider member is eased by low-friction polymeric bearing strips. The slide guide track is provided in a pair of opposing faces with respective vertical slots formed by pairs of inwardly oriented vertical flanges. The bearing strips are inserted into the slots. The bearing strips are made of non-lubricated low-friction polymeric material and each comprise an inner flange and an outer flange connected to one another via a bight or bridging section to define a pair of oppositely facing vertical grooves. These grooves receive respective flanges of the slide guide track to hold the bearing strips to the slide guide track. Each slot of the guide track receives a plurality of bearing strips stacked one on top of the other. The repair and maintenance of this slide guide assembly and particularly of the bearing strips requires disruption of the sludge treatment process because it requires draining the tank to reach a level where the lower bearing strips can be pulled out of the guide track. This task necessitates reaching into the digester tank with long hooks to retrieve the bearing strips that are located in the submerged portion of the guide channel. Even then removal may be frustrated by dirt and debris lodged in the track. Moreover, this operation requires the use of safety equipment and/or multiple personnel.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to a vertical slide guide assembly for a floating cover of a sludge digester tank and contemplates the provision of a slide guide assembly that may be more easily serviced and maintained than conventional slide guide assemblies.

[0008] A slide guide assembly for a floating cover of a sludge digester tank comprises, in accordance with the present invention, a track having at least one surface defining an at least partially vertical guide path and at least one slider member slidably engaged with the track for motion along the path. The track is connected at least indirectly to one of the floating cover and the tank, while the slider member is connected at least indirectly to the other of the tank and the floating cover. At least one bearing strip is attached to the slider member for engaging the surface of the track in a low-friction slidable contact. The bearing strip is removable from the slider member while the slider member remains in slidable engagement with the track.

[0009] In a particular embodiment of the present invention, the sliding surface of the slide guide track is one of a pair of opposing surfaces of the track facing one another to define the path as an at least partially vertical guide channel. The slider member is disposed in the channel for motion therein. The bearing strip is one of at least two bearing strips attached to the slider member for engaging the opposing surfaces of the track in a low-friction slidable contact. The bearing strips are both removable from the slider member while the slider member remains in slidable engagement with the track.

[0010] The bearing strip or strips may be adapted for removal from the slider member in a transverse direction relative to the slider member. Alternatively, the bearing strip or strips are removable in a longitudinal direction, i.e., parallel to a longitudinal axis of the slider member.

[0011] The track may be vertical, with the slider member being disposed for vertical motion along the path. In that case, the bearing strip or strips are preferentially removed vertically from the slider member. Alternatively, the track may be spiral and define an inclined or partially vertical path for the slider member.

[0012] Pursuant to specific features of the present invention, cooperating connector elements are provided on the slider member and the one or more bearing strips for enabling removal of each bearing strip from the slider member by moving the respective bearing strip in a longitudinal direction along the slider member. The connector elements exemplarily include mating flanges and grooves disposed in parallel planes. The flanges may be disposed on the slider member and the grooves on the bearing strip or strips. Each bearing strip may be formed with two oppositely facing grooves, while the slider member is provided on a side with a pair of flanges inserted into respective ones of the oppositely facing grooves.

[0013] Where the slider member is formed with a pair of opposing flanges disposed in a common plane oriented vertically, a respective bearing strip is formed with a pair of oppositely facing vertical grooves receiving respective ones of the flanges.

[0014] Preferably, the bearing strip or strips are made of a non-lubricated polymeric material.

[0015] The present invention is directed in part to a slider kit for use in a slide guide assembly for a floating cover of a sludge digester tank. The kit comprises at least one slider member and at least one bearing strip. The slider member is disposable along an at least partially vertical guide track for at least partially vertical motion therealong. The slider member has a longitudinal axis and is connectable at least indirectly to the tank or the floating cover. Each of the one or more bearing strips is attachable to the slider member along a side thereof for engaging a surface of the track in a low-friction slidable contact. The bearing strip or strips are attachable to and removable from the slider member while the slider member remains in slidable engagement with the track.

[0016] As discussed above, the bearing strip or strips may be slidably attachable to the slider member for relative motion parallel to the longitudinal axis of the slider member. In that case, cooperating connector elements are provided on the slider member and the bearing strip(s) for enabling a removal of the bearing strip(s) from the slider member by moving the bearing strip(s) parallel to the longitudinal axis of the slider member. The connector elements may include flanges and grooves, provided, for example, on the slider member and the bearing strip(s), respectively. More particularly, each bearing strip may be formed with two oppositely facing grooves, while the slider member is provided with a pair of flanges insertable into respective ones of the oppositely facing grooves.

[0017] Alternatively, the bearing strip or strips may be removable transversely from the slider member.

[0018] A method for repairing or maintaining a slide guide assembly for a floating cover of a sludge digester tank comprises, in accordance with the present invention, removing a first bearing strip from a slider member of the slide guide assembly, the slider member being rigidly attached at least indirectly to the floating cover or the sludge digester tank, providing a second bearing strip, and attaching the second bearing strip to the slider member at a location previously occupied by the first bearing strip.

[0019] The removing of the first bearing strip from the slider member preferably includes sliding the first bearing strip longitudinally along the slider member until the first bearing strip is completely removed from the slider member. The attaching of the second bearing strip to the slider member preferably includes inserting a lower end of the second bearing strip into the slider member, and thereupon sliding the second bearing strip longitudinally along and into the slider member. The floating cover is maintained in an operative position in the sludge digester tank during the sliding of the first bearing strip, the inserting of the lower end of the second bearing strip, and the sliding of the second bearing strip.

[0020] A sludge digester tank system, comprises, in accordance with the present invention, a tank, a floating cover slidably mounted to the tank, and at least one slide guide assembly connected to the tank or the cover. The guide assembly includes a track defining an at least partially vertical guide path and at least one slider member slidably engaged with the track for at least partially vertical motion therealong, the track being connected at least indirectly to the tank or the cover while the slider member is connected at least indirectly to the cover or the tank. The guide assembly further includes at least one bearing strip attached to the slider member for engaging a surface of the track in a low-friction slidable contact. The bearing strip is removable from the slider member while the slider member remains in slidable engagement with the track. The various features of the slide guide assembly are discussed above.

[0021] The present invention provides a slide guide assembly for a floating cover of a sludge digester tank, which is more easily serviced and maintained than conventional slide guide assemblies. This is particularly the case for digester covers with a long range of travel, where the replaceable bearing strips are mounted to the slider member.

[0022] In a slide guide assembly, in accordance with the present invention, for a floating cover of a sludge digester tank, repair and maintenance operations may be effectuated by a single individual, without interrupting the sludge digestion process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a vertical cross-sectional view of a gas holding digester cover with a slide guide assembly in accordance with the present invention.

[0024]FIG. 2 is a side elevational view of a slide guide assembly in accordance with the present invention, showing the slide guide assembly connected to a skirt of a digester tank cover.

[0025]FIG. 3 is a front elevational view of a track in the slide guide assembly of FIG. 4.

[0026]FIG. 4 is a partial front elevational view, on a larger scale, of a modified track in accordance with the present invention.

[0027]FIG. 5 is a top plan view of the track of FIG. 4, showing a slider member disposed in a guide channel of the track.

[0028]FIG. 6 is a top plan view, on a larger scale, of the slider member of FIG. 5, showing removable bearing strips in accordance with the present invention.

[0029]FIG. 7 is a schematic partial elevational view of a digester tank cover and a spiral slide guide assembly in accordance with the present invention.

[0030]FIG. 8 is a schematic broken-away perspective view of a digester tank wall, floating tank cover and a spiral slide guide assembly in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The term “floating cover” is used herein to denote sludge digester tank covers that are either floating digester covers or gas holding digester covers.

[0032] The phrase “at least partially vertical” is used herein to denote a direction of extension that is either entirely vertical or inclined with respect to the vertical and the horizontal. An “at least partially vertical” track or channel may be linear or arcuate, for instance, spiral. In the latter case, the track or channel is necessarily partially vertical.

[0033] The term “longitudinal direction” as used herein refers to a direction along or parallel to an elongate member or channel.

[0034] As depicted in FIG. 1, a gas holding digester cover 10 includes a dome-shaped cover plate 12 supporting a manhole conduit 14 with a lid 16, a center ring 18, and a sample well 22. Well 22 is braced by an angle support 26. Cover plate 12 is provided along its periphery with a downwardly depending skirt 28. Along an outer side of skirt 28 is provided a plurality of circumferentially spaced slide guide assemblies 30, 32 which are connected to the skirt for enabling a vertical movement of cover plate 12 during a sludge processing operation. Along an inner side of skirt 28 are provided a series of concrete ballast blocks 34, 36 suspended in part by respective angle supports 38, 40. The tank wall 42, 44 buttresses slide guide assemblies 30, 32 and skirt 28.

[0035]FIG. 2 is a partial depiction of a gas holding digester cover 50 including a dome-shaped cover plate 52 provided along its periphery with a downwardly depending skirt 54 and, radially inwardly thereof, a side sheet stiffener 55. A plurality of circumferentially spaced slide guide assemblies 56 (only one shown) along an outer side of skirt 54 are connected to the skirt for enabling a vertical movement of cover plate 52 in response to variations in the amount of sludge and gas in the sludge digester tank. The tank wall 58 buttresses slide guide assemblies 56 and skirt 54. Slide guide assemblies 56 each include a track 62 and a slider member 64. Slider member 64 is fixed to skirt 54 via coupling brackets 66 and 68 and is slidably disposed in a vertical channel 70 (FIG. 3) defined between two extruded profile elements 72 and 74 of track 62. Track 62 is bolted at spaced locations 76 and 78 to tank wall 58 and to a brace 82 (FIG. 2) atop the column.

[0036]FIG. 4 depicts a track 88 wherein a vertical channel 90 is formed by a backing plate 92 and two extruded beams 94 and 96. Track 88 is provided with vertical flanges or tongues 102, 104 and horizontal flanges or tongues 106, 108 (FIG. 5) to provide an anchoring surface for a travel limiting member (not shown) of the slider assembly.

[0037]FIG. 5 depicts a slide guide assembly 110 include track 88 and a slider member 112 slidably disposed in channel 90 for vertical movement with a floating or gas holding digester tank cover as discussed above reference to FIGS. 1 and 2. FIG. 6 depicts a slider member 112 having a first pair of opposing vertical flanges 114, 116 defining a vertical slot 118 on one side and a second pair of opposing vertical flanges 120, 122 defining a vertical slot 124 on an opposite side. Received in slots 118 and 124 are respective bearing strips 126 and 128.

[0038] Bearing strips 126 and 128 are made of a non-lubricated polymeric material and have low-friction contact surfaces 130 and 132 (see FIG. 6) which face inwardly oriented surfaces 134 and 136 of guide member beams 94 and 96 (FIG. 5). As shown in FIG. 6, bearing strips 126 and 128 each comprise an inner flange 138 and an outer flange 140 connected to one another via a bight or bridging section 142 to define a pair of oppositely facing vertical grooves 144 and 146. Grooves 144 and 146 receive flanges 114, 116 or 120, 122 in mating cooperation to hold bearing strips 126 and 128 to slider member 112. Flanges 140 may be provided along an inwardly facing side with beveled edges 148 for facilitating insertion or removal procedures.

[0039] Bearing strips 126, 128 may be removed from slider member 112 by sliding the bearing strips in a vertically upward direction relative to the slider member 112 and guide member or track 88 (FIG. 5). Removal of bearing strips 126, 128 may be executed by a single individual, while the digester tank cover plate 12 (FIG. 1), 52 (FIG. 2) and the associated skirt 28 (FIG. 1), 54 (FIG. 2) are maintained in an operational position. New bearing strips 126, 128 may then be inserted into the upper ends of slots 118 and 124, so that flanges 114, 116 and 120, 122 are inserted into the grooves 144, 146 of the respective new bearing strips.

[0040] As illustrated in FIG. 7, a slide guide assembly 150 may include a track or rail 152 that spirals around a digester tank 154. One or more spiral slider members 156 fixed to a floating cover 158 of the digester tank are slidably disposed in a spiral channel 160 of the guide track 152. Each slider member 156 is fixed to the top of the cover 158 and is preferably 2 to 3 feet long. Each slider member 156 is provided on a lower side with at least one bearing strip 162 of a non-lubricated low-friction material such as polytetrafluoroethylene. Bearing strip 162 contacts an upwardly facing sliding surface 166 of track 152. Each slider member 156 may also be provided along an upper side with one or more bearing strips 164 of a non-lubricated low-friction material. Bearing strips 162 and 164 may be arcuate, with a curve matching that of slider member 156. Alternatively, bearing strips 162 and 164 may possess a certain flexibility for bending along an arcuate extent of slider member 156.

[0041] As illustrated in FIG. 8, a track 168 of a slider assembly 170 may be fastened to a tank cover 172 rather than a tank wall 174. In that event, a slider member 176 is mounted to the tank wall 174, for instance, on a rim 178 thereof via a bracket 180. Slider member 176 is provided with bearing strips 182 and 184 removable by simply sliding the bearing strips along the track 168 while the slider member 176 remains in position in the track.

[0042] Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. For instance, a low-friction bearing strip of a slider assembly in accordance with the invention may take another form such as a channel or U-shaped member in which a slider member is inserted. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof. 

What is claimed is:
 1. A slide guide assembly for a floating cover of a sludge digester tank, comprising: a track having at least one surface defining an at least partially vertical guide path, said track being connected at least indirectly to one of the floating cover and the tank; at least one slider member slidably engaged with said track for motion along said path, said slider member being connected at least indirectly to the other of the floating cover and the tank; and at least one bearing strip attached to said slider member for engaging said surface of said track in a low-friction slidable contact, said bearing strip being removable from said slider member while said slider member remains in slidable engagement with said track.
 2. The slide guide assembly defined in claim 1 wherein said surface is one of a pair of opposing surfaces of said track facing one another to define said path as an at least partially vertical guide channel, said slider member being disposed in said channel for motion therein, said bearing strip is one of at least two bearing strips attached to said slider member for engaging said opposing surfaces of said track in a low-friction slidable contact, said bearing strips being removable from said slider member while said slider member remains in slidable engagement with said track.
 3. The slide guide assembly defined in claim 2 wherein cooperating connector elements are provided on said slider member and each one of said bearing strips for enabling removal of said bearing strips from said slider member by moving said bearing strips in a longitudinal direction along said slider member.
 4. The slide guide assembly defined in claim 3 wherein said connector elements include mating flanges and grooves.
 5. The slide guide assembly defined in claim 4 wherein said flanges and said grooves are disposed in parallel planes.
 6. The slide guide assembly defined in claim 5 wherein said flanges are on said slider member and said grooves are on said bearing strips.
 7. The slide guide assembly defined in claim 6 wherein each of said bearing strips has two oppositely facing grooves and wherein said slider member is provided on the respective side with a pair of flanges inserted into respective ones of said oppositely facing grooves.
 8. The slide guide assembly defined in claim 2 wherein said slider member is formed with a pair of opposing flanges disposed in a common plane oriented vertically and parallel to said opposing surfaces, each of said bearing strips being formed with a pair of oppositely facing vertical grooves receiving respective ones of said flanges.
 9. The slide guide assembly defined in claim 1 wherein said path extends vertically, said slider member being disposed for vertical motion along said path.
 10. The slide guide assembly defined in claim 9 wherein said bearing strip is vertically removable from said slider member.
 11. The slide guide assembly defined in claim 1 wherein said bearing strip is made of a non-lubricated polymeric material.
 12. A slider kit for use in a slide guide assembly for a floating cover of a sludge digester tank, comprising: at least one slider member disposable along an at least partially vertical guide track for at least partially vertical motion therealong, said slider member being connectable at least indirectly to one of the floating cover and the digester tank, said slider member having a longitudinal axis; and at least one bearing strip attachable to said slider member along a side thereof for engaging a surface of said track in a low-friction slidable contact, said bearing strip being removably attachable to said slider member.
 13. The slider kit defined in claim 12 wherein said bearing strip is slidably attachable to said slider member for removal motion in a direction parallel to said longitudinal axis.
 14. The slider kit defined in claim 13 wherein cooperating connector elements are provided on said slider member and said bearing strip for enabling a removal of said bearing strip from said slider member by moving said bearing strip parallel to said longitudinal axis.
 15. The slider kit defined in claim 14 wherein said connector elements include flanges and grooves.
 16. The slider kit defined in claim 15 wherein said flanges are provided on said slider member and said grooves are provided on said bearing strips.
 17. The slider kit defined in claim 16 wherein said bearing strip has two oppositely facing grooves and wherein said slider member is provided with a pair of flanges insertable into respective ones of said oppositely facing grooves.
 18. The slider kit defined in claim 13 wherein said slider member is formed with a pair of opposing flanges disposed in a common plane oriented parallel to said longitudinal axis, said bearing strip being formed with a pair of oppositely facing grooves for receiving respective ones of said flanges.
 19. The slider kit defined in claim 12 wherein said bearing strip is made of a non-lubricated polymeric material.
 20. A method for repairing or maintaining a slide guide assembly for a floating cover of a sludge digester tank, comprising: removing a first bearing strip from a slider member of the slide guide assembly, said slider member being attached at least indirectly to one of the floating cover and the sludge digester tank, said slider member being disposed in slidable engagement with a track fastened to the other of said floating cover and said sludge digester tank, the removing of said first bearing strip being executed while said slider member remains in slidable engagement with said track; providing a second bearing strip; and while said slider member remains in slidable engagement with said track, attaching said second bearing strip to said slider member at a location previously occupied by said first bearing strip.
 21. The method defined in claim 20 wherein the removing of said first bearing strip from said slider member includes sliding said first bearing strip longitudinally along said slider member until said first bearing strip is completely removed from said slider member, and wherein the attaching of said second bearing strip to said slider member includes: inserting a lower end of said second bearing strip into said slider member; and upon inserting of said lower end, sliding said second bearing strip longitudinally along and into said slider member.
 22. The method defined in claim 21, further comprising maintaining said floating cover in an operative position in said sludge digester tank during the sliding of said first bearing strip, the inserting of said lower end of said second bearing strip, and the sliding of said second bearing strip.
 23. A sludge digester tank system, comprising: a tank; a floating cover movably mounted to said tank; and at least one slide guide assembly operatively connected to said tank and said cover, said guide assembly including: a track defining an at least partially vertical guide path, said track being connected at least indirectly to one of the tank and the cover; at least one slider member slidably engaged with said track for at least partially vertical motion therealong, said slider member being connected at least indirectly to the other of the tank and the cover; and at least one bearing strip attached to said slider member for engaging a surface of said track in a low-friction slidable contact, said bearing strip being removable from said slider member while said slider member remains in slidable engagement with said track.
 24. The sludge digester tank system defined in claim 23 wherein said surface is one of a pair of opposing surfaces of said track facing one another to define said path as an at least partially vertical guide channel, said slider member being disposed in said channel for at least partially vertical motion therein, said bearing strip being one of at least two bearing strips attached to said slider member for engaging said opposing surfaces of said track in a low-friction slidable contact, said bearing strips being vertically removable from said slider member.
 25. The sludge digester tank system defined in claim 24 wherein cooperating connector elements are provided on said slider member and each one of said bearing strips for enabling removal of said bearing strips from said slider member by moving said bearing strips in a vertical direction relative to said slider member.
 26. The sludge digester tank system defined in claim 25 wherein said connector elements include mating flanges and grooves.
 27. The sludge digester tank system defined in claim 26 wherein said flanges and said grooves are disposed in vertical planes.
 28. The sludge digester tank system defined in claim 26 wherein said flanges are on said slider member and said grooves are on said bearing strips.
 29. The sludge digester tank system defined in claim 23 wherein said slider member is formed with a pair of opposing flanges disposed in a common plane oriented vertically and parallel to said opposing surfaces, said bearing strip being formed with a pair of oppositely facing vertical grooves receiving respective ones of said flanges. 